1. Field of the Invention
The present invention relates to a data transmission method and apparatus therefor, for dividing information data, such as on-demand broadcast signal data, into a plurality of data segments and for transmitting each of the data segments formed in a divided manner through individual data transmission channels, and to a data receiving method and apparatus therefor, for receiving data transmitted by such a data transmission method or apparatus therefor.
2. Description of the Related Art
A method has been proposed in which, in television broadcasts in which movies or recorded images/audio are content, content desired on the receiving side at a desired time can be received. A broadcast in such a method is called a “broadcast of an on-demand method (on-demand broadcast)”. With remarkable developments in digital technology in both areas of hardware and software and heavy diversification of content which is broadcast, the present situation is that such on-demand broadcasts are expected to become widely used.
In data transmission using the on-demand form such as on-demand broadcasts, information data representing content to be broadcast is made to be, for example, encoded data on which a predetermined coding process is performed. When performing data processing for the transmission of the encoded data, for data division, generally, two techniques are used, and for data transmission, generally, two techniques are used.
One of the two techniques regarding data division is an equal-length division technique for dividing encoded data representing various types of content into a plurality of data segments having an equal time length. The other technique is an unequal-length division technique for dividing encoded data representing various types of content into a plurality of data segments having a gradually increasing time length. Furthermore, one of the two techniques regarding data transmission is a repeated transmission technique for converting each of a plurality of data segments, formed as a result of encoded data representing various types of content being divided, into segmented packet data in order to form a plurality of segmented packet data and for repeatedly transmitting each of the segmented packet data. The other technique is a continuous transmission technique for obtaining continuous packet data by performing specific coding on each of a plurality of data segments, formed as a result of encoded data representing various types of content being divided, in order to form a plurality of continuous packet data and for continuously transmitting each of the continuous packet data.
FIG. 12 is a timing chart which conceptually shows an example of data transmission of an on-demand form in which an equal-length division technique and a repeated transmission technique are used. In this example, encoded data representing predetermined content to be transmitted is divided into p data segments DS1 to DSp having an equal time length.
The data segment DS1 which is formed in a divided manner is converted into segmented packet data DP1. The segmented packet data DP1 is formed as packet stream data on which a predetermined coding process is performed. Then, the segmented packet data DP1 is repeatedly transmitted through a data transmission channel CH1.
In a similar manner, the data segments DS2 to DSp which are formed in a divided manner are converted into segmented packet data DP2 to DPp which is packet stream data, respectively, on which a predetermined coding process is performed. Then, the segmented packet data DP2 to DPp is repeatedly transmitted through data transmission channels CH2 to CHp, respectively.
In this manner, the segmented packet data DP1 to DPp which is repeatedly transmitted through individual data transmission channels (each of the data transmission channels CH1 to CHp) forms transmission data of p channels. On the receiving side, at any desired time, the segmented packet data DP1 to DPp sent as transmission data of p channels are received in sequence, the data segments DS1 to DSp which are based on the received segmented packet data DP1 to DPp, respectively, are obtained, these data segments are sent in sequence, and the encoded data representing the original content is reproduced.
FIG. 13 is a timing chart which conceptually shows an example of data transmission of an on-demand form in which an equal-length division technique and a continuous transmission technique are used. Also in this example, encoded data representing predetermined content to be transmitted is divided into p data segments DS1 to DSp having an equal time length.
As a result of a specific coding process being performed on the data segment DS1 which is formed in a divided manner, the data segment DS1 is converted into continuous packet data DLT1 which is composed of a continuous packet stream. For a specific coding process in such a case, a special coding process (hereinafter referred to as an “LT coding process”) is used in which, for example, a packet stream with nearly infinite continuousness is formed so as to be capable of reproducing the original data segment DS1 from, for example, one of the portions having the amount of data corresponding to approximately 105% of the data segment DS1 (portion of a predetermined amount of data) within that packet stream. Then, the continuous packet data DLT1 is continuously transmitted through the data transmission channel CH1.
In a similar manner, as a result of, for example, a specific coding process, which is an LT coding process, being performed on each of the data segments DS2 to DSp which are formed in a divided manner, the data segments DS2 to DSp are converted into continuous packet data DLT2 to DLTp, each of which is composed of a continuous packet stream. Then, the continuous packet data DLT2 to DLTp is continuously transmitted through data transmission channels CH2 to CHp, respectively.
In this manner, the continuous packet data DLT1 to DLTp which is transmitted through individual data transmission channels (each of the data transmission channels CH1 to CHp) forms transmission data of p channels. On the receiving side, at any desired time, a portion of a predetermined amount of data in each of the continuous packet data DLT1 to DLTp, sent as transmission data of p channels, is received in sequence, the data segments DS1 to DSp based on the portion of a predetermined amount of data in each of the received continuous packet data DLT1 to DLTp, respectively, are obtained, these data segments are sent in sequence, and the encoded data representing the original content is reproduced.
FIG. 14 is a timing chart which conceptually shows an example of data transmission of an on-demand form in which an unequal-length division technique and a repeated transmission technique are used. In this example, encoded data representing predetermined content to be transmitted is divided into q data segments DS1 to DSq having a gradually increasing time length.
The data segment DS1 which is formed in a divided manner so as to have the shortest time length is converted into segmented packet data DP1. The segmented packet data DP1 is formed as packet stream data on which a predetermined coding process is performed. Then, the segmented packet data DP1 is repeatedly transmitted through the data transmission channel CH1.
The data segments DS2 to DSq which are formed in a divided manner so as to be longer than the time length of the data segment DS1 and so as to have gradually increasing time lengths are also converted into segmented packet data DP2 to DPq, which is formed as packet stream data on which a predetermined coding process is performed, respectively. Then, the segmented packet data DP2 to DPq is repeatedly transmitted through data transmission channels CH2 to CHq, respectively.
In this manner, the segmented packet data DP1 to DPq which is repeatedly transmitted through individual data transmission channels (each of the data transmission channels CH1 to CHp) forms transmission data of q channels. On the receiving side, at any desired time, the segmented packet data DP1 to DPq sent as transmission data of q channels is received in sequence, the data segments DS1 to DSq which are based on the received segmented packet data DP1 to DPq, respectively, are obtained, these data segments are sent in sequence, and the encoded data representing the original content is reproduced.
FIG. 15 is a timing chart which conceptually shows an example of data transmission of an on-demand form in which an unequal-length division technique and a continuous transmission technique are used. Also in this example, encoded data representing predetermined content to be transmitted is divided into q data segments DS1 to DSq having a gradually increasing time length.
The data segment DS1 which is formed in a divided manner so as to have the shortest time length is converted into continuous packet data DLT1 composed of a continuous packet stream, for example, as a result of a specific coding process which is an LT coding process being performed thereon. Then, the continuous packet data DLT1 is continuously transmitted through the data transmission channel CH1.
In a similar manner, the data segments DS2 to DSq which are formed in a divided manner so as to be longer than the time length of the data segment DS1 and so as to have a gradually increasing time length are also converted into continuous packet data DLT2 to DLTq, each of which is composed of a continuous packet stream, as a result of a specific coding process which is an LT coding process being performed on each of the data segments. Then, the continuous packet data DLT2 to DLTQ is continuously transmitted through the data transmission channels CH2 to CHq, respectively.
In this manner, the continuous packet data DLT1 to DLTq which is transmitted through individual data transmission channels (each of the data transmission channels CH1 to CHq) forms transmission data of q channels. On the receiving side, at any desired time, the portion of a predetermined amount of data in each of the continuous packet data DLT1 to DLTQ sent as transmission data of q channels is received in sequence, the data segments DS1 to DSq which are based on the portion of the predetermined amount of data in each of the received continuous packet data DLT1 to DLTq, respectively, are obtained, these data segments are sent in sequence, and the encoded data representing the original content is reproduced.
In either case of the data transmission of the on-demand form using an equal-length division technique, such as an example of which is shown in FIGS. 12 and 13 and the data transmission of the on-demand form using an unequal-length division technique, such as an example of which is shown in FIGS. 14 and 15, on the receiving side, reproduction of the data segment DS1 is performed after the reception of the portion of the predetermined amount of data in the segmented packet data DP1 or the continuous packet data DLT1 is completed. In a similar manner, the reproduction of each of the data segments DS2 to DSp or the data segments DS2 to DSq is also performed after the reception of the portion of the predetermined amount of data in the continuous packet data DLT2 to DLTp or in the continuous packet data DLT2 to DLTq is completed. Therefore, on the receiving side, when the reception of the predetermined amount of data in the segmented packet data DP1 or the continuous packet data DLT1 is completed, the reproduction of the data segments DS1 to DSp or the data segments DS1 to DSq is started, and in order to make the reproduction start waiting time for the data segments DS1 to DSp or the data segments DS1 to DSq short, the time length of the data segment DS1 is made relatively short.
Therefore, in the case of the data transmission of the on-demand form using the equal-length division technique, each of the data segments DS1 to DSp is made to have a relatively short time length. As a result, the number of data divisions for the encoded data representing the content to be transmitted becomes relatively large, and the number of data transmission channels becomes relatively large.
In contrast, in the case of the data transmission of the on-demand form using the unequal-length division technique, the time length of the data segment DS1 is made to be relatively short, but the time length of each of the data segments DS2 to DSq is gradually increased. As a result, the number of data divisions for the encoded data representing content to be transmitted is less than that in the case of the data transmission of the on-demand form using the equal-length division technique, and a lesser number of data transmission channels is required. Therefore, from the viewpoint of reducing the number of data transmission channels, data transmission of the on-demand form using the unequal-length division technique is desirable.
In such a situation, in the data transmission of the on-demand form, when content to be transmitted is so-called live information, such as live performance information, live program information, live broadcast information, etc., on the receiving side, after the start time of the live information (the start time of a live performance, a live program, a live broadcast, etc.), a reproduction start waiting time up to the time encoded data representing content which is that live information (live content) can be reproduced from the beginning occurs.
FIG. 16 is a timing chart showing an example of data transmission of an on-demand form in which content to be transmitted is live information. In this example, an unequal-length division technique is used to reduce the number of data transmission channels, and a repeated transmission technique is used.
In the case of such an example shown in FIG. 16, encoded data representing live content is divided into r data segments DS1 to DSr having a gradually increasing time length. At a live information start time t1, encoded data representing live content begins to be formed, and repeated transmission of the segmented packet data DP1 based on the data segment DS1, through the data transmission channel CH1, is started. Thereafter, repeated transmission of the segmented packet data DP2 to DPr based on the data segments DS2 to DSr, through the data transmission channels CH2 to CHr, respectively, is started in sequence.
On the receiving side, at time t4 when the reception of data which arrives first within the segmented packet data DPr which is repeatedly transmitted through the data transmission channel CHr, is completed, the reproduction of the data segment DSr based on the received segmented packet data DPr can be started. Therefore, time t2 obtained by calculating backwards, from time t4, the corresponding time lengths of the data segments DSr−1 to DS1 reproduced before time t4, is assumed to be a time when the reproduction of the data segment DS1 based on the segmented packet data DP1 is started, and after the reproduction of the data segment DS1, the reproduction of the data segments DS2 to DSr based on the segmented packet data DP2 to DPr is performed in sequence. That is, from time t2, the data segments DS1 to DSr can be reproduced continuously from the beginning.
In such a situation, a reproduction start waiting time Tv from the live information start time t1 to the time t2 occurs. For a person who reproduces the data segments DS1 to DSr on the reproduction side, it is preferable that such a reproduction start waiting time Tv be as short as possible.
The time t4, which is a reference for determining the reproduction start waiting time Tv, is a time when the encoded data representing live content ends. Therefore, the reproduction start waiting time Tv from time t1 to time t2 is made to be equal to the time length of the data segment DSr, which begins to be reproduced at time t4. The data segment DSr is a segment with the maximum time length among the data segments DS1 to DSr. Therefore, the reproduction start waiting time Tv from time t1 to time t2 becomes a relatively long time, and the condition such that the reproduction start waiting time is preferably as short as possible for a person who reproduces the data segments DS1 to DSr cannot be satisfied.
FIG. 17 is a timing chart showing another example of data transmission of an on-demand form in which content to be transmitted is live information. In this example, an unequal-length division technique is used to reduce the number of data transmission channels, and a continuous transmission technique is used.
Also in the case of such an example as shown in FIG. 17, encoded data representing live content is divided into r data segments DS1 to DSr having a gradually increasing time length. At a live information start time t5, encoded data representing live content begins to be formed, and when the formation of the data segment DS1 is completed after the live information start time t5, the transmission of the continuous packet data DLT1 based on the data segment DS1, through the data transmission channel CH1, is started. Thereafter, when the formation of each of the data segments DS2 to DSr is completed, transmission of the continuous packet data DLT2 to DLTr based on the data segments DS2 to DSr, through the data transmission channels CH2 to CHr, respectively, is started in sequence.
On the receiving side, at a time t8 when the reception of the portion of the predetermined amount of data of the continuous packet data DLTr, which is obtained first, which is transmitted through the data transmission channel CHr, the reproduction of the data segment DSr based on the portion of the predetermined amount of data in the received continuous packet data DLTr can be started. Therefore, a time t6, which is obtained by calculating backwards, from time t8, each of the time lengths of the data segments DSr−1 to DS1 reproduced before time t8, is assumed to be a time when the reproduction of the data segment DS1 based on the portion of the predetermined amount of data in the continuous packet data DLT1 is started, and after the reproduction of the data segment DS1, the reproduction of the data segments DS2 to DSr based on the portion of the predetermined amount of data in each of the continuous packet data DLT2 to DLTr is performed in sequence. That is, from time t6, the data segments DS1 to DSr can be reproduced continuously from the beginning.
In such a situation, a reproduction start waiting time Tw from the live information start time t5 to time t6 occurs. Of course, for a person who reproduces the data segments DS1 to DSr on the reproduction side, such a reproduction start waiting time Tw is a time which is preferably as short as possible.
The time t8 which is a reference for determining the reproduction start waiting time Tw is a time such that a time corresponding to the time length of the portion of the predetermined amount of data of the continuous packet data DLTr, which is obtained first, has passed from the time t7 when the encoded data representing live content ends. Therefore, the reproduction start waiting time Tw from time t5 to time t6 is made to be equal to the sum of the time length of the portion of the predetermined amount of data, which is obtained first, of the continuous packet data DLTr which is begun to be sent at time t7 and the time length of the data segment DSr whose reproduction is started at time t8. The data segment DSr is a segment that has the maximum time length among the data segments DS1 to DSr. Therefore, the reproduction start waiting time Tw from time t5 to time t6 becomes a relatively long time, and the condition such that the reproduction start waiting time be as short as possible for the person who reproduces the data segments DS1 to DSr cannot be satisfied.